Statement-1 :An important feature of Fluorite structures is that cations being large in size occupy FCC lattice points whereas anions occupy all the tetrahedral voids giving the formula unit AB2(A : cation, B : anion).Statement-2 :There are 6 cations and 12 anions per FCC unit cell of the Fluorite structure.a)Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1.b)Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1.c)Statement-1 is True, Statement-2 is False.d)Statement-1 is False, Statement-2 is TrueCorrect answer is option 'C'. Can you explain this answer?

Question

Answer

Statement-1: An important feature of Fluorite structures is that cations being large in size occupy FCC lattice points whereas anions occupy all the tetrahedral voids giving the formula unit AB2 (A: cation, B: anion).
Statement-2: There are 6 cations and 12 anions per FCC unit cell of the Fluorite structure.

Explanation:

Fluorite Structure:
The fluorite structure is a type of crystal structure commonly found in compounds like calcium fluoride (CaF2) and other similar compounds. It is a cubic close-packed (CCP) structure with anions occupying all the tetrahedral voids and cations occupying the face-centered cubic (FCC) lattice points.

Statement-1:
An important feature of Fluorite structures is that cations, which are larger in size, occupy the FCC lattice points. This means that the cations are located at the corners and centers of each face of the unit cell. On the other hand, anions occupy all the tetrahedral voids, which are the spaces between the cations. The formula unit for the fluorite structure is AB2, where A represents the cation and B represents the anion.

Statement-2:
In an FCC unit cell of the fluorite structure, there are 6 cations and 12 anions. This can be determined by analyzing the arrangement of cations and anions in the unit cell. Since the FCC unit cell has 8 corners and each corner is shared by 8 unit cells, there are a total of 8 x 1/8 = 1 cation per unit cell. Additionally, since the FCC unit cell has 6 faces and each face is shared by 2 unit cells, there are a total of 6 x 1/2 = 3 cations per unit cell. Therefore, the total number of cations in an FCC unit cell of the fluorite structure is 1 + 3 = 4.

Similarly, for anions, each tetrahedral void is shared by 4 unit cells. Since there are 4 tetrahedral voids in an FCC unit cell, there are a total of 4 x 1/4 = 1 anion per unit cell. Additionally, each face of the unit cell is shared by 2 tetrahedral voids. Since there are 6 faces in an FCC unit cell, there are a total of 6 x 1/2 = 3 anions per unit cell. Therefore, the total number of anions in an FCC unit cell of the fluorite structure is 1 + 3 = 4.

From the above analysis, it is clear that there are 4 cations and 4 anions in an FCC unit cell of the fluorite structure, which contradicts Statement-2. Hence, Statement-2 is false.

Conclusion:
Based on the explanations above, Statement-1 is true, but Statement-2 is false. Therefore, the correct answer is option 'c' - Statement-1 is true, Statement-2 is false.

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